This invention relates to a static pressure gas bearing spindle assembly for use in the inspection of optical and magnetic disks.
A conventional static pressure gas bearing spindle assembly is shown in FIG. 2. It includes a housing 30 having a sleeve mounting hole 31 in which two bearing sleeves 32 and 33 are mounted one over the other. A chuck sleeve 34 is mounted between the bearing sleeves 32 and 33. A spindle 35 is inserted through the sleeves 32, 33 and 34. Between the spindle 35 and the respective sleeves 32 and 33 are provided radial bearing gaps 36. The bearing sleeves 32, 33 have nozzles 37 through which compressed gas is jetted into the radial gaps 36.
The spindle 35 carries at its top end a table 38 and at its bottom end a thrust plate 39 that opposes a flange 33a provided at the bottom end of the lower bearing sleeve 33. A bearing plate 40 is provided opposite to the bottom surface of the thrust plate 39. The bearing plate 40 and the flange 33a of the bearing sleeve 33 have nozzles 42 through which compressed gas is jetted into thrust bearing gaps 41 formed between the thrust plate 39 and the bearing plate 40 and between the thrust plate 39 and the flange 33a, respectively.
The chuck sleeve 34 is formed with a suction passage 43 that communicates with a disk suction recess 38a formed in the table 38.
In operation, a workpiece such as an optical disk or a magnetic disk is sucked to the table 38. Then, compressed gas is jetted through the nozzles 37 and 42 in to the radial bearing gaps 36 and the thrust bearing gaps 41 so that the spindle 35 is supported by a film of gas formed in the gaps 36, 41. In this state, the spindle 35 is rotated at a high speed to inspect the workpiece carried on the table.
Such a conventional static pressure gas bearing spindle assembly has annular gas exhaust spaces 44 between the chuck sleeve 34 and the two bearing sleeves 32, 33. Also, the housing 30 has a gas exhaust passage 45 that communicates with the gas exhaust spaces 44. Compressed gas supplied into the radial bearing gaps 36 and the thrust bearing gaps 41 is thus exhausted through the gas exhaust passage 45.
The radial bearing gap 36 formed between the upper bearing sleeve 32 and the spindle 35 communicates with the space between the bottom surface of the table 38 and the top surface of the housing 30. Thus, compressed gas supplied into the radial bearing gaps 36 tends to flow upwards and leak out through the space between the table 38 and the housing 30. In order to prevent such gas leakage, a cover 46 is provided on the top surface of the housing 30. But such a cover cannot completely prevent the leakage of gas.
If the compressed gas supplied into the bearing gaps contain dust, such dust may adhere to the workpiece carried on the table 38 and thus make inspection of the workpiece inaccurate.
An object of this invention is to provide a static pressure gas bearing spindle assembly which can prevent the leakage of compressed gas supplied into the bearing gap and thus can prevent any dust contained in the compressed gas from adhering to the workpiece supported on the table, such as a disk.